Discovery of the human cytomegalovirus-specific peptide repertoire naturally processed and presented by infected human antigen presenting cells

Background

Infection with or reactivation of human cytomegalovirus (HCMV) remains a clinically problem in immunocompromised patients mainly caused by insufficient T-cell functionality. Knowledge of viral targets is critical to improve monitoring of high-risk patients and to optimize antiviral T-cell therapy. We aimed to identify naturally presented HLA-A*11:01-restricted HCMV-derived T-cell epitopes from HCMV-infected professional antigen presenting cells to expand the spectrum of immunogenic targets.

Methods

Monocyte-derived and genetically-engineered induced dendritic cells (iDCs) were generated to provide a stable platform for soluble (s)HLA-A*11:01 production. After infection of sHLA-A*11:01-secreting cells with wild type HCMV or a mutant lacking known immune evasion molecules (US2-6+11), sHLA-A*11:01-bound peptides were isolated by w6/32 immunoaffinity chromatography followed by mass spectrometric analysis. Identified peptides were screened for their viral protein origin and binding strength to HLA-A*11:01 using established databases. The highest scoring candidates were selected for in vitro evaluation of immunogenicity, cytotoxicity, clinical relevance and suitability for immune monitoring.

Results

More than 50 naturally presented candidate peptides were identified. The immunogenicity of the 25 highest scoring HLA-A*11:01-restricted peptides was evaluated, with functional active CMV-specific T cells detected against five candidates in healthy CMV⁺ donors by IFN-γ-EliSpot. Their complex stability was demonstrated by in vitro peptide binding assays. Highly proliferative and cytotoxic memory T cells were detected after stimulation with the UL36-derived A11_SAL and UL122-derived A11_SVS peptides in healthy CMV⁺ donors and HCMV-infected patients. Surprisingly, A11_SAL-specific memory T cells exhibited functional properties at levels comparable to those T cells against the known immunodominant pp65-derived A02_NLV peptide.

Conclusion

Eliciting strong antiviral T-cell responses in healthy CMV⁺ donors as well as HCMV-infected patients, the A11_SAL peptide was identified as a new major target of the anti-HCMV immune response. Newly identified HCMV peptides expand the repertoire of immunodominant targets and will improve strategies for identification of high-risk patients, and enhancing therapeutic options using HCMV-specific T cells.

Offenlegung Interessenkonflikt:

The authors declare no conflict of interest.